Mechanical properties of recovered municipal solid waste incineration bottom ash: the influence of ageing and changes in moisture content

The scarcity of non-renewable natural resources and the demand for waste recycling and utilisation steer towards increased use of waste-derived materials in civil engineering structures. However, as the quality of different waste-derived materials can vary depending on input materials and processes in which they are generated, the utilisation of these materials in civil engineering may be risky and cumbersome unless their properties are well known. In Finland, due to the recently increased number of waste incineration plants, nearly 300,000 t of municipal solid waste incineration bottom ash (MSWI BA) is generated annually in the country. As the material is mainly landfilled or used in landfill site structures at the moment, the utilisation of MSWI BA in different civil engineering applications could be increased, if the essential properties of the material were properly understood. In this study, the mechanical properties of recovered MSWI BA were investigated with cyclic load and static triaxial tests. The study focused especially on the influence of changes in moisture content and its relation to the development of recovered MSWI BA stiffness and strength properties over time. The obtained results showed that the stiffness of recovered MSWI BA was highly affected by the changes in moisture content over time but also the material ageing had an influence. The resilient modulus, M-r, was at least doubled during the two months' storage of test specimens. Furthermore, when the MSWI BA material dried out and the moisture content decreased 5-7%, the resilient modulus, M-r, of the material was even quadrupled.